Pupil diameter does not covary with learning during single-session Neurofeedback Training

One of the major challenges in neurofeedback (NFB) research is that a large proportion of users have difficulty or cannot learn to control their neural activity when provided feedback. Studying learning from a fundamental perspective, using independent measures, during NFB training is crucial to address this challenge. Our aim in this study was to investigate whether the pupil diameter can be used as a biomarker for learning neural self-regulation. Twenty healthy subjects performed four sessions of NFB training to control different electroencephalogram (EEG) power features. We did not observe any differences in pupil diameter across NFB sessions between learners and non-learners. In addition, no correlation was found between the pupil diameter and the targeted EEG power features during NFB training for all subjects. Our results indicate that the pupil diameter does not covary with learning neural self-regulation, possibly due to confounding factors such as mental fatigue. Further studies are needed to explore whether other eye-related parameters can be linked to learning during NFB training.